1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light (herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays and gamma-rays and the like).
2. Description of the Prior Art
Photoconductive materials constituting photoconductive layers for solid state image pick-up devices, electrophotographic image forming members in the field of image formation, or manuscript reading devices are required to have a high sensitivity, a high SN ratio (Photocurrent (Ip)/Dark Current (Id)), absorption spectral characteristics matching to the spectral characteristics of irradiating electromagnetic waves, a good response to light, a desired dark resistance value as well as being safe to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should be easily treated within a predetermined time. In particular, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid safety characteristic is very important.
From the standpoint as mentioned above, amorphous silicon (hereinafter referred to as "a-Si") has recently attracted attention as a photoconductive material. For example, German Laid-Open Patent Publication Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and German Laid-Open Patent Publication No. 2933411 discloses application of a-Si for use in a photoelectric converting reading device.
However, under the present situation, although the photoconductive members having photoconductive layers constituted of a-Si of the prior art have been attempted to be improved with respect to individual characteristics, including various electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and response to light, environmental characteristics in use, and further stability with lapse of time and durability, there exists room for further improvement in their overall characteristics.
For instance, when the a-Si photoconductor is applied to an image forming member for an electrophotographic device, residual potential is frequently observed to remain during use thereon especially if increases in both photosensitivity and dark resistance are contemplated.
When such a photoconductive member is repeatedly used for a long time, there will be caused various problems such as accumulation of residual charge by repeated uses or so-called ghost phenomenon wherein residual images are formed.
Further, a-Si materials may contain as constituent atoms hydrogen atoms or halogen atoms such as fluorine atoms, chlorine atoms, etc. for improving their electrical, photoconductive characteristics, and boron atoms, phosphorus atoms, etc. for controlling the electroconductivity type, and further other atoms for improving other characteristics. Depending on the manner in which these constituent atoms are contained, there may sometimes be caused problems with respect to electrical, or photoconductive characteristics, or dielectric strength of the layer formed.
For example, there are such problems as shown hereafter. The life of photocarriers produced in the photoconductive layer by irradiation is not long enough. Injection of electric charge from the support side can not be prevented sufficiently. Images transferred to a receiving paper often suffer from defective images, so-called "blank areas", caused by a local discharge breakdown. When a blade is used for cleaning, another defective image, so-called "white lines", are produced which seem to be produced due to rubbing with the blade. Further, when the photoconductive layer is used in a highly humid atmosphere or is used directly after standing in a highly humid atmosphere for a long time, there are often produced disadvantageous so-called "unfocused images".
Further, when the layer thickness becomes ten microns or thicker and then, the member is taken out of a vacuum deposition chamber and exposed to air, the layer is liable to peel off from the support or crack with the lapse of time. These undesirable phenomena occur, in particular, where the support is a drum-like support used in electrophotographic techniques. Accordingly, there still exists problems as to stability with lapse of time.
Thus, it is required in designing a photoconductive material to make efforts to overcome all of such problems as mentioned above along with the improvement of a-Si materials per se.
In view of the above points, the present invention contemplates the discoveries made as a result of extensive studies comprehensively made from the standpoints of applicability and utility of a-Si as a photoconductive member for image forming members for electrophotography, solid state pick-up devices and reading devices etc. It has now been found that a photoconductive member having a photoconductive layer comprising a-Si, in particular, an amorphous material constituted of at least one of hydrogen atom (H) and halogen atom (X) in a matrix of silicon (hereinafter referred to comprehensively as a-Si (H, X)), (for example, so-called hydrogenated amorphous silicon, halogenated amorphous silicon or halogen-containing hydrogenated amorphous silicon), exhibits not only practical and extremely good characteristics, but also surpasses conventional photoconductive members in substantially all aspects, provided that the photoconductive member is constituted to have a specific layer structure as explained in the following. The photoconductive member has markedly excellent characteristics for electrophotography.
The present invention is based on the above mentioned discovery.